The invention relates to a flat display device comprising a first substrate, at least one electron source and a second substrate spaced apart from the first substrate by at least one spacer made of an organic polymer.
The invention also relates to a method of manufacturing such a display device.
Flat display devices of this type are used as display panels in, for example, portable computers, and in other applications where the use of cathode ray tubes may give rise to problems. Moreover, there is increasing interest in using flat display devices in video applications.
A flat display device of the type mentioned above is described in PCT/WO-90/00808. In the device spacers made of polyimide are manufactured by coating a substrate with a layer comprising a polyamide ester, subsequently drying this layer and patterning it photolithographically (exposure to ultraviolet radiation, followed by development). After further treatment, polyimide spacers having a height of 100 to 150 .mu.m are obtained.
However, the above-described display device has a number of drawbacks. For example, the inside of the display panel (second substrate) is provided with phosphors and with a conducting layer of, for example, aluminium or indium-tin oxide for the purpose of transporting electrons. To obtain a satisfactory display, for example, in television applications, an accelerating voltage of the order of 2 to 5 kV is required (dependent on the materials used, gas filling, etc.) between the first substrate (where electron sources in the form of field emitters are present in said device) and the second substrate. Such high accelerating voltages this may lead to graphite formation via flash-over in the vicinity of the organic chemical spacer material (polyimide), so that both the vacuum and the electrical behaviour of the device may be influenced detrimentally. Though it is possible to prevent this by providing the spacers with a suitable coating (for example, chromium oxide or silicon oxide), this requires additional process steps, such as vapour deposition while simultaneously rotating the substrate, or preferential precipitation from a liquid, while protecting the substrate from the treatment.
Another drawback of the device shown in PCT/WO-90/00808 is that an adjacent pixel may be excited by backscattered or secondary electrons.